[luoguP1963] [NOI2009]变换序列（二分图最大匹配）

传送门

根据公式xjb推一下，然后就可以连边。

考虑到字典序最小，和匈牙利算法的实现过程，要倒序匹配。

#include <cmath>
#include <cstdio>
#include <vector>
#include <cstring>
#include <iostream>
#include <algorithm>
#define N 40001

using namespace std;

int n, cnt;
int head[N], to[N], nex[N], belong[N], a[N];
bool vis[N];
vector <int> vec;

inline int read()
{
	int x = 0, f = 1;
	char ch = getchar();
	for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -1;
	for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - '0';
	return x * f;
}

inline bool check(int x, int y, int d)
{
	return 0 <= x && x < n && min(abs(x - y), n - abs(x - y)) == d;
}

inline void add(int x, int y)
{
	to[cnt] = y;
	nex[cnt] = head[x];
	head[x] = cnt++;
}

inline bool dfs(int u)
{
	int i, v;
	for(i = head[u]; ~i; i = nex[i])
	{
		v = to[i];
		if(!vis[v])
		{
			vis[v] = 1;
			if(!belong[v] || dfs(belong[v]))
			{
				belong[v] = u;
				return 1;
			}
		}
	}
	return 0;
}

inline bool solve()
{
	int i, ans = 0;
	for(i = n - 1; i >= 0; i--)
	{
		memset(vis, 0, sizeof(vis));
		ans += dfs(i);
	}
	return ans == n;
}

int main()
{
	int i, j, x, d;
	n = read();
	memset(head, -1, sizeof(head));
	for(i = 0; i < n; i++)
	{
		d = read();
		vec.clear();
		x = d + i;
		if(check(x, i, d)) vec.push_back(x);
		x = n - d + i;
		if(check(x, i, d)) vec.push_back(x);
		x = i - d;
		if(check(x, i, d)) vec.push_back(x);
		x = i - n + d;
		if(check(x, i, d)) vec.push_back(x);
		sort(vec.begin(), vec.end());
		if(vec.size()) for(j = vec.size() - 1; j >= 0; j--) add(i, vec[j]);
	}
	if(!solve()) puts("No Answer");
	else
	{
		for(i = 0; i < n; i++) a[belong[i]] = i;
		for(i = 0; i < n; i++) printf("%d ", a[i]);
	}
	return 0;
}